1. Field of the Invention
Exemplary embodiments of the present invention relates to a phosphor sheet, a light-emitting device having the phosphor sheet, and a method of manufacturing the same.
2. Discussion of the Background
A light-emitting diode (LED) is a semiconductor light-emitting device that emits light when electrons and holes are re-combined with each other in a P-N junction structure, by applying current. LEDs operate at a low voltage and have a long lifespan and low cost characteristics. Conventionally, LEDs have mainly been used in a limited number of applications. However, recently, LEDs have been used in various applications, such as in display devices, illumination devices, vehicle lights, projectors, or the like, due to the development of an industrial technology, particularly, the development of an information display technology and semiconductor technology.
A light-emitting device may implement white light by combining an LED chip with a phosphor. For example, the light-emitting device may implement white light by a combination of a blue LED chip made of a semiconductor component emitting light having a wavelength of 430 to 480 nm, and a yellow yttrium aluminum garnet (YAG)-based phosphor capable of emitting yellow light when excited by the light of the blue LED chip.
Conventional light-emitting devices have mainly used a scheme of applying a resin composition, in which a yellow phosphor and an epoxy resin or a silicon resin are mixed, to an upper portion of a blue LED chip, or sealing the LED chip using the resin composition. However, the qualities of the emitted light are significantly affected by the application of a method of applying the phosphor and operating conditions of the LED chip. In addition, there are many difficulties in reproducing the same white light, luminance is irregular, and color reproduction is deteriorated, due to a mixing ratio of a phosphor and a resin, thermal instability of this resin, irregular deposition of a phosphor at the time of curing of a resin composition, and the like.
Therefore, instead of a method of molding a resin containing a phosphor, a method of disposing a layer or a sheet including a phosphor on an upper portion of an LED chip has been recently attempted. However, when the phosphor sheet is formed to have the same area as that of the upper portion of the LED chip, light emitted from a side of the LED chip may not be efficiently incident to the phosphor sheet. When the phosphor sheet is formed to be larger than the upper portion of the LED chip, in order to solve this problem, it is not easy to align the LED chip and the phosphor sheet with each other, such that the color of emitted light is not uniform, due to the misalignment. In addition, when the light emitted from the LED chip is diffusion-reflected, due to collision with phosphor particles dispersed in an inner portion of the phosphor sheet, back to the LED chip, light emission efficiency is reduced.